php实现等比例不失真缩放上传图片的方法

<?php
function resizeImage($im,$maxwidth,$maxheight,$name,$filetype)
 {
 $pic_width = imagesx($im);
 $pic_height = imagesy($im);
 if(($maxwidth && $pic_width > $maxwidth) || ($maxheight && $pic_height > $maxheight))
 {
  if($maxwidth && $pic_width>$maxwidth)
  {
  $widthratio = $maxwidth/$pic_width;
  $resizewidth_tag = true;
  }
  if($maxheight && $pic_height>$maxheight)
  {
  $heightratio = $maxheight/$pic_height;
  $resizeheight_tag = true;
  }
  if($resizewidth_tag && $resizeheight_tag)
  {
  if($widthratio<$heightratio)
   $ratio = $widthratio;
  else
   $ratio = $heightratio;
  }
  if($resizewidth_tag && !$resizeheight_tag)
  $ratio = $widthratio;
  if($resizeheight_tag && !$resizewidth_tag)
  $ratio = $heightratio;
  $newwidth = $pic_width * $ratio;
  $newheight = $pic_height * $ratio;
  if(function_exists("imagecopyresampled"))
  {
  $newim = imagecreatetruecolor($newwidth,$newheight);//PHP系统函数
   imagecopyresampled($newim,$im,0,0,0,0,$newwidth,$newheight,$pic_width,$pic_height);//PHP系统函数
  }
  else
  {
  $newim = imagecreate($newwidth,$newheight);
   imagecopyresized($newim,$im,0,0,0,0,$newwidth,$newheight,$pic_width,$pic_height);
  }
  $name = $name.$filetype;
  imagejpeg($newim,$name);
  imagedestroy($newim);
 }
 else
 {
  $name = $name.$filetype;
  imagejpeg($im,$name);
 }
 }
//使用方法：
$im=imagecreatefromjpeg("./20140416103023202.jpg");//参数是图片的存方路径
$maxwidth="600";//设置图片的最大宽度
$maxheight="400";//设置图片的最大高度
$name="123";//图片的名称，随便取吧
$filetype=".jpg";//图片类型
resizeImage($im,$maxwidth,$maxheight,$name,$filetype);//调用上面的函数